Examples 3-2 and 3-3 show SOAP messages with s:mustUnderstand=1 for the
wsa:To header, but not for any other header. The SOAP binding says
nothing about the mustUnderstand header at all. If mustUnderstand is
meant to reflect that the wsa:To header is mandatory, it should be
present on the wsa:Action as well, but more likely this is just an
oversight and the s:mustUnderstand attribute should be removed to avoid
muddying the waters.